1. Field of the Invention
The present invention relates to a method for mounting of an elongated member inside an elongated, elastic, flexible tubing, initially having an inside cross sectional dimension being about the same size as or smaller than the outside cross sectional dimension of the elongated member.
The invention also relates to a device for performing the mounting.
2. Description of the Prior Art
In different contexts it is desirable to provide an elongated member of some kind, with a shielding layer of an elastic material. This can sometimes be carried out by forming the shielding layer directly onto the elongated member, by for example extrusion. However, in certain cases this kind of operation is not possible to perform for different reasons. Instead the only available option is to insert the elongated member into a flexible tubing of the desired material.
In the field of for example medical implantable leads, it is known to insert or mount an elongated member in form of a metallic coil into a flexible tubing of e.g. silicone. Such leads may preferably be used for pacemaker applications to monitor and pace the activity of a human or animal heart. However, they could also be used for other medical applications, such as for example monitoring, diagnosing or pacing other arbitrary organs inside a body, or for nerve stimulation. The length of such medical implantable leads my vary, but is normally in the range of 40 to 100 cm.
The demands on this kind of medical implantable leads are high. The diameter should be as small as possible, down to about 1 mm in diameter, and they should be highly flexible to be able to be inserted into the body through e.g. narrow blood vessels. When mounting the lead into the body, the lead has to be steerable by means of a steering wire inserted through a bore inside the lead. Moreover, the bore is also utilized when fastening the lead to the desired organ by means of for example a helix in the distal end of the lead, wherein a second, permanently mounted elongated member inside the lead, or a supplementary, temporarily inserted torque transmitting wire is inserted into the bore for performing screw rotation of the helix for screwing it into the tissue and fasten the distal end of the lead to the organ. The coil of the lead should also serve as an electrical conductor for transmitting electrical signals to and from the organ.
The small dimensions as well as the highly flexible characteristics of the coil and the tubing, makes the introducing of the coil into the tubing very difficult. Accordingly, in prior art techniques for performing the assembling, it is known to use different chemical substances, such as for example isopropanol or heptane, serving as a lubricant agent when inserting the coil into the tubing. However, there are some disadvantages associated with this technique. The chemical substances may for instance be unhealthy for the personnel performing the assembling, and they might adversely effect other procedures during the manufacturing, such as gluing. Also, despite the use of lubricating chemical substances, it is still difficult and time consuming to properly insert the coil into the tubing and it is often necessary to use a tubing having an inner cross sectional dimension being larger than desirable to be able to insert the coil into the tubing. This could necessitate the use of an adhesive substance between the coil and the tubing to prevent movement of them in relation to each other during use. It also commonly occurs that the coil will be stretched out or compressed in relation to the tubing during assembling, in which case the assembled coil and tubing has to be relaxed by manually rolling them between hands and a plane surface after assembling.